Acoustic echoes develop, for example, when tones, sounds and noises from a loudspeaker are picked up by a microphone in the same room or in the same acoustic environment. In telecommunication systems, these are transmitted back, as acoustic feedback signals, to the subscriber at the far or other end, who notices them as a delayed version of his own speech. Echo signals here represent a distracting disturbance and may even prevent interactive, bi-directional full-duplex communication. Furthermore, acoustic echoes may also lead to howling effects and other instabilities of the acoustic feedback loop.
Here, the microphone signal picked up by the microphone has differences as compared with the loudspeaker signal supplied to the corresponding loudspeaker, which result from the acoustic environment in which the microphone and the loudspeaker are arranged, on the one hand, and from noise sources originating from the most diverse physical sources, on the other hand. Apart from noise sources of the acoustic environment, the loudspeaker itself, associated circuits, the microphone and other circuits associated therewith, to mention only a few of the potential sources, thus may couple noise into the microphone signal.
The presence of stationary or quasi-stationary noise and noises in the microphone signal here may significantly affect the achievable audio quality of the system.
WO 2006/111370 A1 relates to a method and an apparatus for the removal of an echo in a multi-channel audio signal. Acoustic echo control and noise suppression is an important part of every hands-free telecommunications system, such as telephone, audio or video conferencing systems. Bandwidth limitations and restrictions with respect to the computation complexity also are to be taken into account here. The method of processing multi-channel audio loudspeaker signals and at least one microphone signal described in the document here includes the steps of transforming the input microphone signal into input microphone short-time spectra, computation of a combined loudspeaker signal short-time spectrum from the loudspeaker signals, computation of a combined microphone signal short-time spectrum from the input microphone signal, an estimation of a magnitude spectrum or a power spectrum of the echo in the combined microphone signal short-time spectrum, computation of a gain filter for magnitude modification of the input microphone short-time spectrum, application of the gain filter to at least one input microphone spectrum, and conversion of the filtered input microphone spectrum into the time domain.